1. FIELD OF THE INVENTION:
The present invention relates to a discharge valve apparatus of a compressor.
2. DESCRIPTION OF THE PRIOR ART:
FIGS. 1 and 2 show the conventional discharge valve apparatus of a compressor.
In FIGS. 1 and 2, the reference numeral (1) designates a cylinder of a compressor; (2) designates a piston; (3) designates a valve plate on which a discharge port (4), a suction port (5) and a tapped holes (6) are formed. The reference numeral (7) designates a cylinder cover; (8) designates a discharge plenum; (9) designates a suction valve and (10) designates a long thin discharge valve and the center Q of the long thin discharge valve (10) is disposed on a center line P of the discharge port (4) as shown in FIG. 2. The reference numeral (11) designates through holes formed at the both ends of the long thin discharge valve (10); (12) designates a valve stopper having through holes (13) at the both ends; (14) designates pins which are respectively screwed in the tapped holes formed on the valve plate (3) through the springs (15), the through holes (11) of the valve (10) and the through holes (13) of a valve stopper (12) whereby the valve stopper (12) and the valve (10) are pressed to the valve plate under a specified spring force.
In the conventional discharge valve apparatus having the abovementioned structure, the stress variation as shown in FIG. 3 is caused in the longitudinal direction of the valve (10) on the surface of the valve (10) in the side of valve stopper (12) during one reciprocation of the piston (2).
In FIG. 3, the abscissa shows the time, and the ordinate shows the stress, and the point A on the abscissa shows the time when the piston locates at the top dead point, and the point B shows the time when the piston locates at the bottom dead point and the point C shows the zero stress time when the pressure of the cylinder applied to the valve becomes equal to that of the discharge plenum. During the time from the top dead point A of the piston to the zero stress point C, the pressure of the cylinder is lower than that of the discharge plenum whereby the pressure difference between the discharge plenum and the cylinder is applied inwardly to the part for closing the discharge port (4) by the valve (10) whereas compressive stress proportional to the pressure difference is applied to the external surface of the valve (10) in the side of the valve stopper (12).
In the compression stroke after passing the piston (2) through the bottom dead point B, the pressure of the cylinder gradually increases to be equal to that of the discharge plenum at the time of the point C. The pressure of the cylinder increases further to be higher than the discharge pressure whereby the drag force is applied to the valve (10). When the drag force becomes higher than the total of the resilient force of the valve (10) and the frictional forces among the valve plate (3), the valve (10) and the valve stopper (12) due to the spring force of the springs (15), the valve (10) deforms so as to curve outwardly at the central part while sliding to the horizontal direction at the pressed part and at last, the deformation of the valve (10) is restricted by the valve stopper (12). Accordingly, the tensile stress is applied to the external surface of the valve (10) in the side of the valve stopper (12) during the time from the point C to the next top dead point A' of the piston as shown in FIG. 3. Thus, the compressive stress and the tensile stress are alternatively applied to the external surface of the valve (10) during one reciprocation of the piston (2).
FIG. 4 shows longitudinal stress distribution applied on the external surface of the valve (10) during the time between the point A and the point C of FIG. 3 in the conventional discharge valve apparatus.
In FIG. 4, the reference E designates a point on the valve (10) corresponding to the peripheral part of the discharge port (4) and Q designates a point on the valve (10) corresponding to the center of the discharge port (4).
FIG. 5 shows longitudinal stress distribution applied on the external surface of the valve (10) during the time between the point C and the point A' of FIG. 3 in the conventional discharge valve apparatus.
As it is clear from FIGS. 3, 4 and 5, the largest tensile stress and compressive stress are repeatedly applied at the center Q of the valve (10) during one reciprocation of the piston (2) in the conventional discharge valve apparatus. Accordingly, it is necessary to spend a lot of time for the fabrication of the valve (10) such as punching fabrication and barrel machining for edge surfaces so as to prevent fatigue failure.